Explanation:
When a lemon is kept in water in a bowl and viewed from outside, it appears larger than its actual size. This phenomenon is known as the apparent shift in size due to refraction.

Refraction of Light:
Refraction is the bending of light as it passes from one medium to another. When light travels from one medium to another, its speed changes, causing the light rays to bend. This bending of light is responsible for various optical phenomena, including the apparent shift in size.

Apparent Shift in Size:
When a lemon is placed in water, light rays from the lemon travel through the air and enter the water. As they cross the water-air interface, they change direction due to refraction. The change in direction causes the light rays to converge or bend towards the normal line. This phenomenon is governed by Snell's law.

Explanation of Snell's Law:
Snell's law states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant when light passes from one medium to another. Mathematically, it can be expressed as:
n1 sinθ1 = n2 sinθ2

Where:
- n1 is the refractive index of the first medium (air in this case)
- n2 is the refractive index of the second medium (water in this case)
- θ1 is the angle of incidence
- θ2 is the angle of refraction

Effect on Apparent Size:
When light rays pass from air into water, they bend towards the normal line, and the angle of refraction is smaller than the angle of incidence. Due to this bending, the light rays appear to come from a point closer to the observer's eye than their actual source. This apparent shift in the direction of the light rays leads to an illusion of an enlarged image.

Conclusion:
Therefore, when a lemon kept in water in a bowl is viewed from outside, it appears larger than its actual size due to the phenomenon of refraction. The bending of light rays at the water-air interface causes the apparent shift in size.